A ball lead screw comprising:
- (a) a lead screw (2) having an external periphery with a helicoidal channel (2.1) of a semicircular profile therein which is threaded with a regular pitch, said lead screw (2) further having a crest (2.2) on the external periphery thereof defined between adjacent lines of said helicoidal channel (2.1);
- (b) a nut (3) surrounding said lead screw (2) and having an internal periphery with a helicoidal channel (3.1) of a semicircular profile therein which is threaded with a regular pitch;
- (c) a multiplicity of ball bearings (1) arranged between the two helicoidal channels (2.1, 3.1);
- (d) a deflector (4) fitted in the nut (3) for transferring the ball bearings (1) from an end of one line of the threaded helicoidal channel (3.1) to an end of another line of the threaded helicoidal channel (3.1) so as to form a closed circuit (5) of flowing ball bearings (1) which roll when relative rotation is imparted between said lead screw (2) and said nut (3);
- (e) said nut (3) further including a through hole (6) extending radially therethrough for housing said deflector (4) in the nut (3), said through hole (6) extending between two equal and parallel lengths of said helicoidal channel (3.1) in said nut;
- (f) said deflector (4) including a body (4.1) fitted with perimetrical free play (4.2) in relation to walls of the nut (3) which define said through hole (6), said body including:
- (i) an inside face (8) with a substantially S-shaped groove (7) therein, said groove (7) having two semicircular mouths (9) of a similar shape to the helicoidal channel (3.1) of the nut (3) to permit entry and exit of said ball bearings (1) which run along said groove (7), said groove (7) lightly touching a crest (2.2) of the lead screw (2) which exists between lines of the threaded helicoidal channel (2.1) thereof that have their circuit (5) closed by the deflector (7);
- (ii) walls (4.4) opposite each of the mouths (9) of the S-shaped groove (7);
- (iii) two equal half-spheres (4.3) joined laterally to the body (4.1), each half-sphere (4.3) being joined to a respective wall (4.4) and having a radius equal to the radius of the ball bearings (1) and smaller than the radius of the semicircular helicoidal channel (3.1) of the nut (3), and each half-sphere (4.3) having a flat face (4.5) oriented in the same plane as the inside face (8), said flat face (4.5) being parallel to and associated with free play relative to the external periphery of the lead screw (2), each half-sphere (4.3) having a spherical surface (4.6) supported at a single free mobile contact point (10) against the semicircular profile of a line of the helicoidal channel (3.1) of said nut (3) which is empty of said ball bearings (1), the distance between the body of the deflector (4) and the points of contact (10) of the half-spheres (4.3) being greater than the amount of perimetrical free play (4.2) in relation to walls of the nut (3) which define said through hole (6).